1. Field of the Invention
The present invention relates to a minor-amount release valve for a hand air pump in which air pressure in a cushion device communicated with the hand air pump can be released by a minor amount to adjust the shock-absorbing ability of the cushion device mounted to a bicycle.
2. Description of the Related Art
Some bicycles are equipped with cushion devices in the front forks thereof to absorb shocks during cycling. The cushion devices include springs or air that performs the shock-absorbing function. FIG. 1 of the drawings illustrates a typical pneumatic cushion device that includes a valve 11 and an upper lid 10. Air is pumped into the cushion device by, e.g., a hand air pump via the valve 11. Some hand air pumps are equipped with a release valve to allow release of air inside the cushion device to adjust air pressure. Thus, the shock-absorbing ability of the cushion device can be adjusted. FIG. 2 of the drawings illustrates a release valve for a hand air pump 12. The hand air pump 12 includes a receptacle 16 that communicates with an air chamber (not shown) of a cushion device (not shown) mounted in a bicycle front fork (not shown). The release valve includes a valve seat 13 partially mounted in the receptacle 16 and having a hole 131 communicated the receptacle 16 with atmosphere, and a stem 132 extended through the hole 131. A clearance 135 is defined between the stem 132 and an inner periphery that defines the hole 131 and thus forms an air passage 135. An end of the stem 132 locates in the receptacle 16 and has a flange 134 formed thereon. A seal ring 14 is mounted around the stem 132 and secured to a side of the flange 134. A spring 15 is attached between the flange 134 and an end wall that defines a portion of the receptacle 16 for biasing the stem 132 away from the receptacle 16 such that the seal ring 14 is moved to block the air passage 135. When air pressure in the cushion device is found too high, the user may press a push button 133 attached to the other end of the stem 132 to overcome the spring force and thus unblock the passage 135. Thus, air in the cushion device is released via the receptacle 16 and the air passage 135. It is, however, found that the amount of air released is relatively large in a short time such that the user has to refill air into the cushion device, as the air pressure in the cushion device is relatively high. Control of the air amount to be released by the push button is difficult as the air pressure is high and the spring force is large. The present invention is intended to provide an improved release valve for a hand air pump that mitigates and/or obviates the above problems.